Air traffic at Newark Liberty International Airport was temporarily halted early Tuesday evening after two drones were spotted in the area.

Gregory Martin, a spokesman for the Federal Aviation Administration said the drones were spotted flying near Teterboro Airport around 5 p.m. Teterboro is a general aviation airport about 20 miles north of Newark International. As a precaution, arriving flights at Newark were temporarily held, he said.

Drones can cause severe damage to aircraft in addition to distracting pilots. The drones in the Newark incident were flying at 3,500 feet, officials said.

Passengers reported that some flights were forced to circle the airport before being cleared to land.

Martin said there is a ground stop in place at other airports on flights headed for Newark until the current backlog of arrivals has landed at the airport.

Officials at United Airlines said they were monitoring reports of drone activity in the Newark area but said the impact to its flight operations had been minimal.

“We are working closely with the airport and the FAA to return our operations to normal as quickly as possible,” the airline said.

Earlier this month, officials were forced to halt flights at London’s Heathrow Airport after reports of drone activity. The month before, officials at Gatwick Airport were forced to suspend flights twice in the same week because of reported drone activity.

When a drone collided with a passenger plane over Quebec City last year, the plane landed safely. But officials said a different point of impact could have been devastating.

An earlier version of this post incorrectly stated the day that the drones were spotted near Newark Airport. This post has been updated to note the drones were spotted on Tuesday.